Typically, in a boiling water reactor, a traversing incore probe system (hereinafter, abbreviated as TIP) that moves a traversing probe in a calibration conduit installed in a reactor to measure neutron flux in the rector core. The calibration conduit is connected to a TIP guide tube outside the reactor. The TIP guide tube extends to outside of the primary containment vessel (hereinafter, abbreviated as PCV) and makes the traversing probe stand by outside the reactor at a time other than the measurement time.
Further, in the TIP guide tube outside the PCV, a traversing incore probe valve, such as an isolation valve or a check valve is provided. The traversing incore probe valve is desirably provided with a support to enhance earthquake resistance so as to protect the valve and the pipe against vibration in case of an earthquake. Thus, various valves and pipes of a nuclear plant are provided with a support, as described in Japanese Patent Application Publication No. 61-39559, for example, the entire content of which is incorporated herein by reference.